Thanks, I feel so silly
As I'm reading your reply, I'm like, "oh my gosh, duh". Because that was the other piece, I couldn't understand why I was seeing the HDD in Device Manager (DM) as well. So I jump on DM, assign drive letter and head over to Win Explorer and there she was, drive letter and all! Thanks again for making me look silly
just kidding. Don't you hate that when that happens.
Your BIOS probably recognized this external HDD as Drive 1 or Drive 2, as did the Device Manager. For the OS to ID the HDD, you need to assign a drive letter to it.
Go to Computer Management, then Disk Management and in the lower part of the screen, right click on the listing and choose "Change Driver letter or Paths". Choose a drive letter like E: or G: etc. and give it a Friendly Name, like "External Data". You should also see the Volume Info showing:
NTFS, or FAT32, Healthy, Active.
If there is no file system on the HDD, you need to format it with NTFS.